Distributed PostgreSQL with a ledger you can verify.

-- a fourth server joins as a new, empty shard group
SELECT kingres.add_node('host4', 5432);

-- which moves would even out the buckets per group?
SELECT * FROM kingres.rebalance_plan();

-- move one bucket: copy, catch up with logical replication,
-- then a two-phase switch (detach on the source, attach on the target)
SELECT kingres.move_bucket(1, 17, 3);   -- colocation, bucket, target group

-- drain a server before removing it
SELECT kingres.set_node_property(4, false);  -- should_have_shards

-- one row per inconsistency; no rows when the cluster is sound
SELECT * FROM kingres.check_cluster();
SELECT * FROM kingres.buckets;

CREATE EXTENSION kingres_ledger;

-- append-only by default; 'updatable' keeps every old version provable
SELECT kingres.ledger_enable('public.accounts');
SELECT kingres.ledger_enable('public.balances', 'updatable');

INSERT INTO accounts VALUES (1, 'ada', 100);   -- captured by a trigger

-- a background worker builds a block about every 10 seconds
SELECT kingres.ledger_generate_digest();   -- store the result OUTSIDE the database

-- later: is the chain intact, and does it match the digest I kept?
SELECT * FROM kingres.ledger_verify();             -- no rows when consistent
SELECT kingres.ledger_verify_digest('{...}');

-- prove that one row version is part of the ledger
SELECT kingres.ledger_inclusion_proof('accounts', kingres.ledger_row_hash(a.*))
  FROM accounts a WHERE id = 1;

CREATE EXTENSION kingres_sketch;

-- HyperLogLog: how many distinct visitors?
SELECT kingres_sketch.approx_count_distinct(user_id) FROM events;

-- t-digest: the 99th percentile of latency
SELECT kingres_sketch.approx_percentile(0.99, latency_ms) FROM requests;

-- Space-Saving: the ten most requested paths
SELECT * FROM kingres_sketch.topn_list(
  (SELECT kingres_sketch.topn_add_agg(path) FROM requests), 10);

-- sketches are values: store one per day, merge them later
SELECT kingres_sketch.hll_cardinality(kingres_sketch.hll_union_agg(visitors))
  FROM daily_rollup WHERE day >= '2026-11-01';

CREATE EXTENSION kingres_timepart;

CREATE TABLE events (at timestamptz NOT NULL, payload jsonb)
  PARTITION BY RANGE (at);

-- daily partitions, a week ahead, dropped after 90 days
SELECT kingres.timepart_set_policy('events',
  partition_every => '1 day',
  create_ahead    => '7 days',
  retention       => '90 days');

SELECT * FROM kingres.timepart_plan('events');   -- what a run would do
CALL kingres.timepart_run('events');             -- do it, with a run history

SELECT * FROM kingres.timepart_partitions('events');
SELECT * FROM kingres.timepart_policies;